In this work it is proposed to synthesize and characterize by IR, ESR, and crystallography various metallo porphyrins. These porphyrins belong to the "picket-fence" type developed by Collman and co-workers, but modified in such a way that one arm reaching into the distal pocket will carry a variety of substituents that may promote or prevent hydrogen-bond formation to axially ligated small molecules. The underlying thesis that the mechanism of action of naturally occurring heme proteins is due to the extent of H-bond interaction with the iron ligand substrate in the distal region of the molecule. The investigator will prepare Fe, Mn, and Co derivatives of suitably modified tetraphenyl porphyrins and investigate the IR and EPR spectra of adducts with CO, NO, O2, CN ions, N3 ions, NO2 ions, SCN ions, H2O, etc. Both acidic and basic distal groups will be studied to gauge the effect of protonation on the H-bonding interaction. IR frequencies of adduct ligands will be studied, verified by isotopic substitutions, and noted as a function of the nature of the distal groups. Spin-free systems such as NO- or Co-containing porphyrins will also be subjected to EPR studies. Finally, those compounds in which H-bonding interactions are discerned will be structurally characterized by single crystal x-ray diffractometry to establish the nature of the interaction.